Method for decoding image by using block partitioning in image coding system, and device therefor

ABSTRACT

The method for decoding an image by a decoding device according to the present document may comprise the steps of: acquiring image information comprising partitioning information for a current block; determining, on the basis of the size of the current block, whether to partition the current block; partitioning the current block into subblocks on the basis of the partitioning information, if it is determined that the current block is to be partitioned, and decoding the subblocks; and not partitioning the current block, if it is determined that the current block is not to be partitioned, and decoding the current block, wherein, if the current block is a chroma block, and the size of the current block is at most the minimum size of a chroma block, then it is determined that the current block is not to be partitioned.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the National Stage filing under 35 U.S.C. 371 ofInternational Application No. PCT/KR2019/012196, filed on Sep. 20, 2019,which claims the benefit of U.S. Provisional Application No. 62/734,292filed on Sep. 21, 2018, the contents of which are all herebyincorporated by reference herein in their entirety.

BACKGROUND OF THE DISCLOSURE Field of the Disclosure

The present disclosure relates to a video coding technology, and moreparticularly, to a video decoding method using block partitioning in avideo coding system and an apparatus thereof.

Related Art

Recently, demand for high-resolution, high-quality images such as HD(High Definition) images and UHD (Ultra High Definition) images havebeen increasing in various fields. As the image data has high resolutionand high quality, the amount of information or bits to be transmittedincreases relative to the legacy image data. Therefore, when image datais transmitted using a medium such as a conventional wired/wirelessbroadband line or image data is stored using an existing storage medium,the transmission cost and the storage cost thereof are increased.

Accordingly, there is a need for a highly efficient image compressiontechnique for effectively transmitting, storing, and reproducinginformation of high resolution and high quality images.

SUMMARY

The present disclosure provides a method and device for improving imagecoding efficiency.

The present disclosure also provides a method and device for improvingintra-prediction efficiency.

The present disclosure also provides a method and device for improvingintra-prediction efficiency based on cross component linear model(CCLM).

The present disclosure also provides an efficient encoding and decodingmethod for CCLM prediction, and a device for performing the encoding anddecoding method.

The present disclosure also provides a method and device for selecting aneighbor sample to derive a linear model parameter for CCLM.

In an aspect, a video decoding method performed by a decoding apparatusis provided. The method includes: obtaining image information includingpartitioning information; determining whether a current block ispartitioned based on a size of the current block; and decoding thecurrent block or decoding sub-blocks of the current block based onwhether the determined current block is partitioned, wherein when it isdetermined that the current block is partitioned, the current block ispartitioned into the sub-blocks based on the partitioning information,and the sub-blocks are decoded, wherein when it is determined that thecurrent block is not partitioned, the current block is not partitioned,and the current block is decoded, and wherein when the current block isa chroma block and the size of the current block is less than or equalto a minimum chroma block size, it is determined that the current blockis not partitioned.

In another aspect, a decoding apparatus for performing video decoding isprovided. The device apparatus includes: an entropy decoder obtainingimage information including partitioning information; and a predictordetermining whether a current block is partitioned based on a size ofthe current block and decoding the current block or decoding sub-blocksof the current block based on whether the determined current block ispartitioned, wherein when it is determined that the current block ispartitioned, the current block is partitioned into the sub-blocks basedon the partitioning information, and the sub-blocks are decoded, whereinwhen it is determined that the current block is not partitioned, thecurrent block is not partitioned, and the current block is decoded, andwherein when the current block is a chroma block and the size of thecurrent block is less than or equal to a minimum chroma block size, itis determined that the current block is not partitioned.

In another aspect, a video encoding method performed by an encodingapparatus is provided. The method includes: determining a partition typefor a current block; determining whether to partition the current blockbased on a size of the current block; not partitioning the current blockif the current block is determined not to be partitioned andpartitioning the current block into sub-blocks based on the partitiontype if the current block is determined to be partitioned; and encodingimage information including partitioning information indicating thepartition type for the current block, wherein when the current block isa chroma block and the size of the current block is less than or equalto a minimum chroma block size, it is determined that the current blockis not partitioned.

In another aspect, a video encoding apparatus is provided. The encodingapparatus includes: an image partitioner determining a partition typefor a current block, determining whether to partition the current blockbased on a size of the current block, not partitioning the current blockif the current block is determined not to be partitioned andpartitioning the current block into sub-blocks based on the partitiontype if the current block is determined to be partitioned; and anentropy encoder encoding image information including partitioninginformation indicating the partition type for the current block, whereinwhen the current block is a chroma block and the size of the currentblock is less than or equal to a minimum chroma block size, it isdetermined that the current block is not partitioned.

Advantageous Effects

According to the present disclosure, overall image/video compressionefficiency may be improved.

According to the present disclosure, image coding efficiency may beimproved by effectively performing image partitioning.

According to the present disclosure, it is possible to reduce a worstcase data throughput by limiting partitioning into luma blocks and/orchroma blocks having a specific size or less, thereby effectivelyreducing an encoding and decoding processing rate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 briefly illustrates an example of a video/image coding device towhich embodiments of the present disclosure are applicable.

FIG. 2 is a schematic diagram illustrating a configuration of avideo/image encoding apparatus to which the embodiment(s) of the presentdisclosure may be applied.

FIG. 3 is a schematic diagram illustrating a configuration of avideo/image decoding apparatus to which the embodiment(s) of the presentdisclosure may be applied.

FIG. 4 shows an example of partitioning a block through a QT structure.

FIG. 5 shows an example of partitioning a block through a BT structure.

FIG. 6 shows an example of partitioning a block through a TT structure.

FIG. 7 exemplarily shows a signaling mechanism of partitioninginformation.

FIG. 8 exemplarily shows a partition type in an MTT structure.

FIG. 9 exemplarily shows an embodiment in which partitioning into a 4×4size luma block and a 2×2 size chroma block is prohibited when a size ofan input image is FHD or larger.

FIG. 10 exemplarily shows an embodiment in which a minimum block size isadjusted based on a size of an input image.

FIG. 11 exemplarily shows an embodiment of adjusting a minimum blocksize.

FIG. 12 exemplarily shows an embodiment of determining a minimum blocksize based on signaled minimum block size information.

FIG. 13 schematically shows an image encoding method by an encodingapparatus according to the present disclosure.

FIG. 14 schematically shows an encoding apparatus that performs an imageencoding method according to the present disclosure.

FIG. 15 schematically shows an image decoding method by a decodingapparatus according to the present disclosure.

FIG. 16 schematically shows a decoding apparatus for performing an imagedecoding method according to the present disclosure.

FIG. 17 exemplarily shows a structure diagram of a content streamingsystem to which embodiments of the present disclosure are applied.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The present disclosure may be modified in various forms, and specificembodiments thereof will be described and illustrated in the drawings.However, the embodiments are not intended for limiting the disclosure.The terms used in the following description are used to merely describespecific embodiments but are not intended to limit the disclosure. Anexpression of a singular number includes an expression of the pluralnumber, so long as it is clearly read differently. The terms such as“include” and “have” are intended to indicate that features, numbers,steps, operations, elements, components, or combinations thereof used inthe following description exist and it should be thus understood thatthe possibility of existence or addition of one or more differentfeatures, numbers, steps, operations, elements, components, orcombinations thereof is not excluded.

Meanwhile, elements in the drawings described in the disclosure areindependently drawn for the purpose of convenience for explanation ofdifferent specific functions, and do not mean that the elements areembodied by independent hardware or independent software. For example,two or more elements of the elements may be combined to form a singleelement, or one element may be partitioned into plural elements. Theembodiments in which the elements are combined and/or partitioned belongto the disclosure without departing from the concept of the disclosure.

Hereinafter, embodiments of the present disclosure will be described indetail with reference to the accompanying drawings. In addition, likereference numerals are used to indicate like elements throughout thedrawings, and the same descriptions on the like elements will beomitted.

FIG. 1 briefly illustrates an example of a video/image coding device towhich embodiments of the present disclosure are applicable.

Referring to FIG. 1, a video/image coding system may include a firstdevice (source device) and a second device (receiving device). Thesource device may deliver encoded video/image information or data in theform of a file or streaming to the receiving device via a digitalstorage medium or network.

The source device may include a video source, an encoding apparatus, anda transmitter. The receiving device may include a receiver, a decodingapparatus, and a renderer. The encoding apparatus may be called avideo/image encoding apparatus, and the decoding apparatus may be calleda video/image decoding apparatus. The transmitter may be included in theencoding apparatus. The receiver may be included in the decodingapparatus. The renderer may include a display, and the display may beconfigured as a separate device or an external component.

The video source may acquire video/image through a process of capturing,synthesizing, or generating the video/image. The video source mayinclude a video/image capture device and/or a video/image generatingdevice. The video/image capture device may include, for example, one ormore cameras, video/image archives including previously capturedvideo/images, and the like. The video/image generating device mayinclude, for example, computers, tablets and smartphones, and may(electronically) generate video/images. For example, a virtualvideo/image may be generated through a computer or the like. In thiscase, the video/image capturing process may be replaced by a process ofgenerating related data.

The encoding apparatus may encode input image/image. The encodingapparatus may perform a series of procedures such as prediction,transform, and quantization for compression and coding efficiency. Theencoded data (encoded video/image information) may be output in the formof a bitstream.

The transmitter may transmit the encoded image/image information or dataoutput in the form of a bitstream to the receiver of the receivingdevice through a digital storage medium or a network in the form of afile or streaming. The digital storage medium may include variousstorage mediums such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, and thelike. The transmitter may include an element for generating a media filethrough a predetermined file format and may include an element fortransmission through a broadcast/communication network. The receiver mayreceive/extract the bitstream and transmit the received bitstream to thedecoding apparatus.

The decoding apparatus may decode the video/image by performing a seriesof procedures such as dequantization, inverse transform, and predictioncorresponding to the operation of the encoding apparatus.

The renderer may render the decoded video/image. The renderedvideo/image may be displayed through the display.

Present disclosure relates to video/image coding. For example, themethods/embodiments disclosed in the present disclosure may be appliedto a method disclosed in the versatile video coding (VVC), the EVC(essential video coding) standard, the AOMedia Video 1 (AV1) standard,the 2nd generation of audio video coding standard (AVS2), or the nextgeneration video/image coding standard (ex. H.267 or H.268, etc.).

Present disclosure presents various embodiments of video/image coding,and the embodiments may be performed in combination with each otherunless otherwise mentioned.

In the present disclosure, video may refer to a series of images overtime. Picture generally refers to a unit representing one image in aspecific time zone, and a slice/tile is a unit constituting part of apicture in coding. The slice/tile may include one or more coding treeunits (CTUs). One picture may consist of one or more slices/tiles. Onepicture may consist of one or more tile groups. One tile group mayinclude one or more tiles. A brick may represent a rectangular region ofCTU rows within a tile in a picture. A tile may be partitioned intomultiple bricks, each of which consisting of one or more CTU rows withinthe tile. A tile that is not partitioned into multiple bricks may bealso referred to as a brick. A brick scan is a specific sequentialordering of CTUs partitioning a picture in which the CTUs are orderedconsecutively in CTU raster scan in a brick, bricks within a tile areordered consecutively in a raster scan of the bricks of the tile, andtiles in a picture are ordered consecutively in a raster scan of thetiles of the picture. A tile is a rectangular region of CTUs within aparticular tile column and a particular tile row in a picture. The tilecolumn is a rectangular region of CTUs having a height equal to theheight of the picture and a width specified by syntax elements in thepicture parameter set. The tile row is a rectangular region of CTUshaving a height specified by syntax elements in the picture parameterset and a width equal to the width of the picture. A tile scan is aspecific sequential ordering of CTUs partitioning a picture in which theCTUs are ordered consecutively in CTU raster scan in a tile whereastiles in a picture are ordered consecutively in a raster scan of thetiles of the picture. A slice includes an integer number of bricks of apicture that may be exclusively contained in a single NAL unit. A slicemay consists of either a number of complete tiles or only a consecutivesequence of complete bricks of one tile. Tile groups and slices may beused interchangeably in the present disclosure. For example, in thepresent disclosure, a tile group/tile group header may be called aslice/slice header.

A pixel or a pel may mean a smallest unit constituting one picture (orimage). Also, ‘sample’ may be used as a term corresponding to a pixel. Asample may generally represent a pixel or a value of a pixel, and mayrepresent only a pixel/pixel value of a luma component or only apixel/pixel value of a chroma component.

A unit may represent a basic unit of image processing. The unit mayinclude at least one of a specific region of the picture and informationrelated to the region. One unit may include one luma block and twochroma (ex. cb, cr) blocks. The unit may be used interchangeably withterms such as block or area in some cases. In a general case, an M×Nblock may include samples (or sample arrays) or a set (or array) oftransform coefficients of M columns and N rows.

In the present disclosure, the term “/” and “,” should be interpreted toindicate “and/or.” For instance, the expression “A/B” may mean “A and/orB.” Further, “A, B” may mean “A and/or B.” Further, “A/B/C” may mean “atleast one of A, B, and/or C.” Also, “A/B/C” may mean “at least one of A,B, and/or C.”

Further, in the document, the term “or” should be interpreted toindicate “and/or.” For instance, the expression “A or B” may comprise 1)only A, 2) only B, and/or 3) both A and B. In other words, the term “or”in the present disclosure should be interpreted to indicate“additionally or alternatively.”

FIG. 2 is a schematic diagram illustrating a configuration of avideo/image encoding apparatus to which the embodiment(s) of the presentdisclosure may be applied. Hereinafter, the video encoding apparatus mayinclude an image encoding apparatus.

Referring to FIG. 2, the encoding apparatus 200 includes an imagepartitioner 210, a predictor 220, a residual processor 230, and anentropy encoder 240, an adder 250, a filter 260, and a memory 270. Thepredictor 220 may include an inter predictor 221 and an intra predictor222. The residual processor 230 may include a transformer 232, aquantizer 233, a dequantizer 234, and an inverse transformer 235. Theresidual processor 230 may further include a subtractor 231. The adder250 may be called a reconstructor or a reconstructed block generator.The image partitioner 210, the predictor 220, the residual processor230, the entropy encoder 240, the adder 250, and the filter 260 may beconfigured by at least one hardware component (ex. An encoder chipset orprocessor) according to an embodiment. In addition, the memory 270 mayinclude a decoded picture buffer (DPB) or may be configured by a digitalstorage medium. The hardware component may further include the memory270 as an internal/external component.

The image partitioner 210 may partition an input image (or a picture ora frame) input to the encoding apparatus 200 into one or moreprocessors. For example, the processor may be called a coding unit (CU).In this case, the coding unit may be recursively partitioned accordingto a quad-tree binary-tree ternary-tree (QTBTTT) structure from a codingtree unit (CTU) or a largest coding unit (LCU). For example, one codingunit may be partitioned into a plurality of coding units of a deeperdepth based on a quad tree structure, a binary tree structure, and/or aternary structure. In this case, for example, the quad tree structuremay be applied first and the binary tree structure and/or ternarystructure may be applied later. Alternatively, the binary tree structuremay be applied first. The coding procedure according to the presentdisclosure may be performed based on the final coding unit that is nolonger partitioned. In this case, the largest coding unit may be used asthe final coding unit based on coding efficiency according to imagecharacteristics, or if necessary, the coding unit may be recursivelypartitioned into coding units of deeper depth and a coding unit havingan optimal size may be used as the final coding unit. Here, the codingprocedure may include a procedure of prediction, transform, andreconstruction, which will be described later. As another example, theprocessor may further include a prediction unit (PU) or a transform unit(TU). In this case, the prediction unit and the transform unit may besplit or partitioned from the aforementioned final coding unit. Theprediction unit may be a unit of sample prediction, and the transformunit may be a unit for deriving a transform coefficient and/or a unitfor deriving a residual signal from the transform coefficient.

The unit may be used interchangeably with terms such as block or area insome cases. In a general case, an M×N block may represent a set ofsamples or transform coefficients composed of M columns and N rows. Asample may generally represent a pixel or a value of a pixel, mayrepresent only a pixel/pixel value of a luma component or represent onlya pixel/pixel value of a chroma component. A sample may be used as aterm corresponding to one picture (or image) for a pixel or a pel.

In the encoding apparatus 200, a prediction signal (predicted block,prediction sample array) output from the inter predictor 221 or theintra predictor 222 is subtracted from an input image signal (originalblock, original sample array) to generate a residual signal residualblock, residual sample array), and the generated residual signal istransmitted to the transformer 232. In this case, as shown, a unit forsubtracting a prediction signal (predicted block, prediction samplearray) from the input image signal (original block, original samplearray) in the encoder 200 may be called a subtractor 231. The predictormay perform prediction on a block to be processed (hereinafter, referredto as a current block) and generate a predicted block includingprediction samples for the current block. The predictor may determinewhether intra prediction or inter prediction is applied on a currentblock or CU basis. As described later in the description of eachprediction mode, the predictor may generate various information relatedto prediction, such as prediction mode information, and transmit thegenerated information to the entropy encoder 240. The information on theprediction may be encoded in the entropy encoder 240 and output in theform of a bitstream.

The intra predictor 222 may predict the current block by referring tothe samples in the current picture. The referred samples may be locatedin the neighborhood of the current block or may be located apartaccording to the prediction mode. In the intra prediction, predictionmodes may include a plurality of non-directional modes and a pluralityof directional modes. The non-directional mode may include, for example,a DC mode and a planar mode. The directional mode may include, forexample, 33 directional prediction modes or 65 directional predictionmodes according to the degree of detail of the prediction direction.However, this is merely an example, more or less directional predictionmodes may be used depending on a setting. The intra predictor 222 maydetermine the prediction mode applied to the current block by using aprediction mode applied to a neighboring block.

The inter predictor 221 may derive a predicted block for the currentblock based on a reference block (reference sample array) specified by amotion vector on a reference picture. Here, in order to reduce theamount of motion information transmitted in the inter prediction mode,the motion information may be predicted in units of blocks, sub-blocks,or samples based on correlation of motion information between theneighboring block and the current block. The motion information mayinclude a motion vector and a reference picture index. The motioninformation may further include inter prediction direction (L0prediction, L1 prediction, Bi prediction, etc.) information. In the caseof inter prediction, the neighboring block may include a spatialneighboring block present in the current picture and a temporalneighboring block present in the reference picture. The referencepicture including the reference block and the reference pictureincluding the temporal neighboring block may be the same or different.The temporal neighboring block may be called a collocated referenceblock, a co-located CU (colCU), and the like, and the reference pictureincluding the temporal neighboring block may be called a collocatedpicture (colPic). For example, the inter predictor 221 may configure amotion information candidate list based on neighboring blocks andgenerate information indicating which candidate is used to derive amotion vector and/or a reference picture index of the current block.Inter prediction may be performed based on various prediction modes. Forexample, in the case of a skip mode and a merge mode, the interpredictor 221 may use motion information of the neighboring block asmotion information of the current block. In the skip mode, unlike themerge mode, the residual signal may not be transmitted. In the case ofthe motion vector prediction (MVP) mode, the motion vector of theneighboring block may be used as a motion vector predictor and themotion vector of the current block may be indicated by signaling amotion vector difference.

The predictor 220 may generate a prediction signal based on variousprediction methods described below. For example, the predictor may notonly apply intra prediction or inter prediction to predict one block butalso simultaneously apply both intra prediction and inter prediction.This may be called combined inter and intra prediction (CIIP). Inaddition, the predictor may be based on an intra block copy (IBC)prediction mode or a palette mode for prediction of a block. The IBCprediction mode or palette mode may be used for content image/videocoding of a game or the like, for example, screen content coding (SCC).The IBC basically performs prediction in the current picture but may beperformed similarly to inter prediction in that a reference block isderived in the current picture. That is, the IBC may use at least one ofthe inter prediction techniques described in the present disclosure. Thepalette mode may be considered as an example of intra coding or intraprediction. When the palette mode is applied, a sample value within apicture may be signaled based on information on the palette table andthe palette index.

The prediction signal generated by the predictor (including the interpredictor 221 and/or the intra predictor 222) may be used to generate areconstructed signal or to generate a residual signal. The transformer232 may generate transform coefficients by applying a transformtechnique to the residual signal. For example, the transform techniquemay include at least one of a discrete cosine transform (DCT), adiscrete sine transform (DST), a karhunen-loève transform (KLT), agraph-based transform (GBT), or a conditionally non-linear transform(CNT). Here, the GBT means transform obtained from a graph whenrelationship information between pixels is represented by the graph. TheCNT refers to transform generated based on a prediction signal generatedusing all previously reconstructed pixels. In addition, the transformprocess may be applied to square pixel blocks having the same size ormay be applied to blocks having a variable size rather than square.

The quantizer 233 may quantize the transform coefficients and transmitthem to the entropy encoder 240 and the entropy encoder 240 may encodethe quantized signal (information on the quantized transformcoefficients) and output a bitstream. The information on the quantizedtransform coefficients may be referred to as residual information. Thequantizer 233 may rearrange block type quantized transform coefficientsinto a one-dimensional vector form based on a coefficient scanning orderand generate information on the quantized transform coefficients basedon the quantized transform coefficients in the one-dimensional vectorform. Information on transform coefficients may be generated. Theentropy encoder 240 may perform various encoding methods such as, forexample, exponential Golomb, context-adaptive variable length coding(CAVLC), context-adaptive binary arithmetic coding (CABAC), and thelike. The entropy encoder 240 may encode information necessary forvideo/image reconstruction other than quantized transform coefficients(ex. values of syntax elements, etc.) together or separately. Encodedinformation (ex. encoded video/image information) may be transmitted orstored in units of NALs (network abstraction layer) in the form of abitstream. The video/image information may further include informationon various parameter sets such as an adaptation parameter set (APS), apicture parameter set (PPS), a sequence parameter set (SPS), or a videoparameter set (VPS). In addition, the video/image information mayfurther include general constraint information. In the presentdisclosure, information and/or syntax elements transmitted/signaled fromthe encoding apparatus to the decoding apparatus may be included invideo/picture information. The video/image information may be encodedthrough the above-described encoding procedure and included in thebitstream. The bitstream may be transmitted over a network or may bestored in a digital storage medium. The network may include abroadcasting network and/or a communication network, and the digitalstorage medium may include various storage media such as USB, SD, CD,DVD, Blu-ray, HDD, SSD, and the like. A transmitter (not shown)transmitting a signal output from the entropy encoder 240 and/or astorage unit (not shown) storing the signal may be included asinternal/external element of the encoding apparatus 200, andalternatively, the transmitter may be included in the entropy encoder240.

The quantized transform coefficients output from the quantizer 233 maybe used to generate a prediction signal. For example, the residualsignal (residual block or residual samples) may be reconstructed byapplying dequantization and inverse transform to the quantized transformcoefficients through the dequantizer 234 and the inverse transformer235. The adder 250 adds the reconstructed residual signal to theprediction signal output from the inter predictor 221 or the intrapredictor 222 to generate a reconstructed signal (reconstructed picture,reconstructed block, reconstructed sample array). If there is noresidual for the block to be processed, such as a case where the skipmode is applied, the predicted block may be used as the reconstructedblock. The adder 250 may be called a reconstructor or a reconstructedblock generator. The generated reconstructed signal may be used forintra prediction of a next block to be processed in the current pictureand may be used for inter prediction of a next picture through filteringas described below.

Meanwhile, luma mapping with chroma scaling (LMCS) may be applied duringpicture encoding and/or reconstruction.

The filter 260 may improve subjective/objective image quality byapplying filtering to the reconstructed signal. For example, the filter260 may generate a modified reconstructed picture by applying variousfiltering methods to the reconstructed picture and store the modifiedreconstructed picture in the memory 270, specifically, a DPB of thememory 270. The various filtering methods may include, for example,deblocking filtering, a sample adaptive offset, an adaptive loop filter,a bilateral filter, and the like. The filter 260 may generate variousinformation related to the filtering and transmit the generatedinformation to the entropy encoder 240 as described later in thedescription of each filtering method. The information related to thefiltering may be encoded by the entropy encoder 240 and output in theform of a bitstream.

The modified reconstructed picture transmitted to the memory 270 may beused as the reference picture in the inter predictor 221. When the interprediction is applied through the encoding apparatus, predictionmismatch between the encoding apparatus 200 and the decoding apparatusmay be avoided and encoding efficiency may be improved.

The DPB of the memory 270 DPB may store the modified reconstructedpicture for use as a reference picture in the inter predictor 221. Thememory 270 may store the motion information of the block from which themotion information in the current picture is derived (or encoded) and/orthe motion information of the blocks in the picture that have alreadybeen reconstructed. The stored motion information may be transmitted tothe inter predictor 221 and used as the motion information of thespatial neighboring block or the motion information of the temporalneighboring block. The memory 270 may store reconstructed samples ofreconstructed blocks in the current picture and may transfer thereconstructed samples to the intra predictor 222.

FIG. 3 is a schematic diagram illustrating a configuration of avideo/image decoding apparatus to which the embodiment(s) of the presentdisclosure may be applied.

Referring to FIG. 3, the decoding apparatus 300 may include an entropydecoder 310, a residual processor 320, a predictor 330, an adder 340, afilter 350, a memory 360. The predictor 330 may include an interpredictor 331 and an intra predictor 332. The residual processor 320 mayinclude a dequantizer 321 and an inverse transformer 321. The entropydecoder 310, the residual processor 320, the predictor 330, the adder340, and the filter 350 may be configured by a hardware component (ex. Adecoder chipset or a processor) according to an embodiment. In addition,the memory 360 may include a decoded picture buffer (DPB) or may beconfigured by a digital storage medium. The hardware component mayfurther include the memory 360 as an internal/external component.

When a bitstream including video/image information is input, thedecoding apparatus 300 may reconstruct an image corresponding to aprocess in which the video/image information is processed in theencoding apparatus of FIG. 2. For example, the decoding apparatus 300may derive units/blocks based on block partition related informationobtained from the bitstream. That is, the image partitioner of thedecoding apparatus 300 may partition an input image (or picture, frame)into one or more processing units. The decoding apparatus 300 mayperform decoding using a processor applied in the encoding apparatus.Thus, the processor of decoding may be a coding unit, for example, andthe coding unit may be partitioned according to a quad tree structure,binary tree structure and/or ternary tree structure from the coding treeunit or the largest coding unit. One or more transform units may bederived from the coding unit. The reconstructed image signal decoded andoutput through the decoding apparatus 300 may be reproduced through areproducing apparatus.

The decoding apparatus 300 may receive a signal output from the encodingapparatus of FIG. 2 in the form of a bitstream, and the received signalmay be decoded through the entropy decoder 310. For example, the entropydecoder 310 may parse the bitstream to derive information (ex.video/image information) necessary for image reconstruction (or picturereconstruction). The video/image information may further includeinformation on various parameter sets such as an adaptation parameterset (APS), a picture parameter set (PPS), a sequence parameter set(SPS), or a video parameter set (VPS). In addition, the video/imageinformation may further include general constraint information. Thedecoding apparatus may further decode picture based on the informationon the parameter set and/or the general constraint information.Signaled/received information and/or syntax elements described later inthe present disclosure may be decoded may decode the decoding procedureand obtained from the bitstream. For example, the entropy decoder 310decodes the information in the bitstream based on a coding method suchas exponential Golomb coding, CAVLC, or CABAC, and output syntaxelements required for image reconstruction and quantized values oftransform coefficients for residual. More specifically, the CABACentropy decoding method may receive a bin corresponding to each syntaxelement in the bitstream, determine a context model using a decodingtarget syntax element information, decoding information of a decodingtarget block or information of a symbol/bin decoded in a previous stage,and perform an arithmetic decoding on the bin by predicting aprobability of occurrence of a bin according to the determined contextmodel, and generate a symbol corresponding to the value of each syntaxelement. In this case, the CABAC entropy decoding method may update thecontext model by using the information of the decoded symbol/bin for acontext model of a next symbol/bin after determining the context model.The information related to the prediction among the information decodedby the entropy decoder 310 may be provided to the predictor (the interpredictor 332 and the intra predictor 331), and the residual value onwhich the entropy decoding was performed in the entropy decoder 310,that is, the quantized transform coefficients and related parameterinformation, may be input to the residual processor 320. The residualprocessor 320 may derive the residual signal (the residual block, theresidual samples, the residual sample array). In addition, informationon filtering among information decoded by the entropy decoder 310 may beprovided to the filter 350. Meanwhile, a receiver (not shown) forreceiving a signal output from the encoding apparatus may be furtherconfigured as an internal/external element of the decoding apparatus300, or the receiver may be a component of the entropy decoder 310.Meanwhile, the decoding apparatus according to the present disclosuremay be referred to as a video/image/picture decoding apparatus, and thedecoding apparatus may be classified into an information decoder(video/image/picture information decoder) and a sample decoder(video/image/picture sample decoder). The information decoder mayinclude the entropy decoder 310, and the sample decoder may include atleast one of the dequantizer 321, the inverse transformer 322, the adder340, the filter 350, the memory 360, the inter predictor 332, and theintra predictor 331.

The dequantizer 321 may dequantize the quantized transform coefficientsand output the transform coefficients. The dequantizer 321 may rearrangethe quantized transform coefficients in the form of a two-dimensionalblock form. In this case, the rearrangement may be performed based onthe coefficient scanning order performed in the encoding apparatus. Thedequantizer 321 may perform dequantization on the quantized transformcoefficients by using a quantization parameter (ex. quantization stepsize information) and obtain transform coefficients.

The inverse transformer 322 inversely transforms the transformcoefficients to obtain a residual signal (residual block, residualsample array).

The predictor may perform prediction on the current block and generate apredicted block including prediction samples for the current block. Thepredictor may determine whether intra prediction or inter prediction isapplied to the current block based on the information on the predictionoutput from the entropy decoder 310 and may determine a specificintra/inter prediction mode.

The predictor 320 may generate a prediction signal based on variousprediction methods described below. For example, the predictor may notonly apply intra prediction or inter prediction to predict one block butalso simultaneously apply intra prediction and inter prediction. Thismay be called combined inter and intra prediction (CIIP). In addition,the predictor may be based on an intra block copy (IBC) prediction modeor a palette mode for prediction of a block. The IBC prediction mode orpalette mode may be used for content image/video coding of a game or thelike, for example, screen content coding (SCC). The IBC basicallyperforms prediction in the current picture but may be performedsimilarly to inter prediction in that a reference block is derived inthe current picture. That is, the IBC may use at least one of the interprediction techniques described in the present disclosure. The palettemode may be considered as an example of intra coding or intraprediction. When the palette mode is applied, a sample value within apicture may be signaled based on information on the palette table andthe palette index.

The intra predictor 331 may predict the current block by referring tothe samples in the current picture. The referred samples may be locatedin the neighborhood of the current block or may be located apartaccording to the prediction mode. In the intra prediction, predictionmodes may include a plurality of non-directional modes and a pluralityof directional modes. The intra predictor 331 may determine theprediction mode applied to the current block by using a prediction modeapplied to a neighboring block.

The inter predictor 332 may derive a predicted block for the currentblock based on a reference block (reference sample array) specified by amotion vector on a reference picture. In this case, in order to reducethe amount of motion information transmitted in the inter predictionmode, motion information may be predicted in units of blocks,sub-blocks, or samples based on correlation of motion informationbetween the neighboring block and the current block. The motioninformation may include a motion vector and a reference picture index.The motion information may further include inter prediction direction(L0 prediction, L1 prediction, Bi prediction, etc.) information. In thecase of inter prediction, the neighboring block may include a spatialneighboring block present in the current picture and a temporalneighboring block present in the reference picture. For example, theinter predictor 332 may configure a motion information candidate listbased on neighboring blocks and derive a motion vector of the currentblock and/or a reference picture index based on the received candidateselection information. Inter prediction may be performed based onvarious prediction modes, and the information on the prediction mayinclude information indicating a mode of inter prediction for thecurrent block.

The adder 340 may generate a reconstructed signal (reconstructedpicture, reconstructed block, reconstructed sample array) by adding theobtained residual signal to the prediction signal (predicted block,predicted sample array) output from the predictor (including the interpredictor 332 and/or the intra predictor 331). If there is no residualfor the block to be processed, such as when the skip mode is applied,the predicted block may be used as the reconstructed block.

The adder 340 may be called reconstructor or a reconstructed blockgenerator. The generated reconstructed signal may be used for intraprediction of a next block to be processed in the current picture, maybe output through filtering as described below, or may be used for interprediction of a next picture.

Meanwhile, luma mapping with chroma scaling (LMCS) may be applied in thepicture decoding process.

The filter 350 may improve subjective/objective image quality byapplying filtering to the reconstructed signal. For example, the filter350 may generate a modified reconstructed picture by applying variousfiltering methods to the reconstructed picture and store the modifiedreconstructed picture in the memory 360, specifically, a DPB of thememory 360. The various filtering methods may include, for example,deblocking filtering, a sample adaptive offset, an adaptive loop filter,a bilateral filter, and the like.

The (modified) reconstructed picture stored in the DPB of the memory 360may be used as a reference picture in the inter predictor 332. Thememory 360 may store the motion information of the block from which themotion information in the current picture is derived (or decoded) and/orthe motion information of the blocks in the picture that have alreadybeen reconstructed. The stored motion information may be transmitted tothe inter predictor 260 so as to be utilized as the motion informationof the spatial neighboring block or the motion information of thetemporal neighboring block. The memory 360 may store reconstructedsamples of reconstructed blocks in the current picture and transfer thereconstructed samples to the intra predictor 331.

In the present disclosure, the embodiments described in the filter 260,the inter predictor 221, and the intra predictor 222 of the encodingapparatus 200 may be the same as or respectively applied to correspondto the filter 350, the inter predictor 332, and the intra predictor 331of the decoding apparatus 300. The same may also apply to the unit 332and the intra predictor 331.

Meanwhile, encoding target images of the VVC standard arehigh-resolution images such as UHD and FHD, and hardware is increasinglycomplicated to process the images. For example, when the intraprediction described above is performed in the VVC standard softwareVTM2.0.1, a 128×128-sized coding tree unit (CTU) is used, but a minimumCU block size is 4×4 size for luma blocks and 2×2 size for chromablocks. Therefore, when an UHD image (3840×2160 resolution) is encodedby performing intra prediction through the VTM2.0.1 software, in a worstcase scenario, the UHD image may be partitioned into 518,400 4×4 lumablocks and 1,036,800 2×2 chroma blocks. Here, the worst case mayrepresent a case in which all of the luma components of the UHD imageare encoded into 4×4-sized luma blocks, and all of the chroma componentsare encoded into 2×2-sized chroma blocks. In hardware implementation,data throughput should cover the worst case, which may lead to anincrease in hardware manufacturing cost and hardware delay.

The present disclosure proposes embodiments for solving theabove-described problem.

In an embodiment, a method of solving complexity of hardwareimplementation is proposed by adaptively adjusting the minimum blocksize according to a size of an image size (i.e., resolution). That is,in the present disclosure, an embodiment in which data throughput in theworst case is adjusted by adaptively adjusting the minimum block sizeaccording to a size of an image to control the amount of data throughputin the worst case is proposed. Here, the block may represent a codingunit (CU), a prediction unit (PU), or a transform unit (TU).

Meanwhile, experimental results for an image in which a 4×4-sized lumablock and a 2×2-sized chroma block are limited on the VTM2.0.1 softwaremay be derived as shown in the following table. That is, the experimentmay represent coding of an image in which the minimum size of the lumablock is 4×8 size/8×4 size and the minimum size of the chroma block is2×4 size/4×2 size. In addition, the following table may showexperimental results for images of all resolutions.

TABLE 1 Over VTM-2.0.1 Y U V EncT DecT All Intra Main10 Class A1 0.10%0.01% −0.07%  92% 97% Class A2 0.12% 0.04% −0.01%  90% 97% Class B 0.30%0.15% 0.17% 88% 93% Class C 1.08% 0.71% 0.90% 85% 91% Class E 0.63%0.12% 0.25% 91% 99% Overall 0.46% 0.23% 0.28% 88% 95% Class D 1.42%1.27% 1.03% 83% 90% Class F (optional) #VALUE! #VALUE! #VALUE! #DIV/0!#DIV/0! Random Access Main 10 Class A1 0.06% 0.03% 0.17% 98% 99% ClassA2 0.15% 0.02% 0.04% 94% 97% Class B 0.25% 0.34% 0.44% 95% 97% Class C0.89% 1.20% 1.37% 94% 92% Class E Overall 0.36% 0.45% 0.55% 95% 96%Class D 1.42% 1.58% 2.16% 91% 88% Class F (optional) #VALUE! #VALUE!#VALUE! #DIV/0! #DIV/0! Low delay B Main10 Class A1 Class A2 Class B0.12% −0.03%  0.26% 98% 104%  Class C 0.66% 0.73% 0.89% 96% 110%  ClassE 0.08% −0.52%  −0.24%  101%  109%  Overall 0.29% 0.10% 0.34% 98% 107% Class D 1.07% 1.74% 1.88% 93% 115%  Class F (optional) #VALUE! #VALUE!#VALUE! #DIV/0! #DIV/0!

Referring to Table 1, encoding loss of Y 0.46% in the all intraexperiment, Y 0.36% in a random access experiment, and Y 0.29% in a lowdelay B experiment. may be derived. However, by limiting the 4×4-sizedluma block and the 2×2-sized chroma block, the worst case datathroughput may be halved and the encoding and decoding processing ratemay be reduced.

In addition, experimental results for UHD and FHD images (i.e.,high-resolution images) in which a 4×4-sized luma block and a 2×2-sizedchroma block are limited may be derived as shown in the following table.That is, the experiment may represent coding of UHD and FHD images(i.e., high-resolution images) in which a minimum size of the luma blockis 4×8 size/8×4 size and a minimum size of the chroma block is 2×4size/4×2 size.

TABLE Over VTM-2.0.1 Y U V EncT DecT All Intra Main10 Class A1 0.10%0.01% −0.07% 92% 97% Class A2 0.12% 0.04% −0.01% 90% 97% Class B 0.30%0.15% 0.17% 88% 93% Overall 0.19% 0.08% 0.06% 89% 95% Random Access Main10 Class A1 0.06% 0.03% 0.17% 98% 99% Class A2 0.15% 0.02% 0.04% 94% 97%Class B 0.25% 0.34% 0.44% 95% 97% Overall 0.17% 0.17% 0.26% 96% 98% Lowdelay B Main10 Class B 0.12% −0.03% 0.26% 98% 104%  Overall 0.12% −0.03%0.26% 98% 104% 

Referring to Table 2 above, Y 0.19% in all intra experiments for UHD andFHD experimental images, Y 0.17% in random access experiments, and Y0.12% low delay B experiments may be derived. Accordingly, it can beenseen that the method of limiting the minimum block size is moreeffective in coding for a high-resolution image, which is an encodingtarget of the VVC standard.

Based on the experimental results described above, the presentembodiment proposes a method of adaptively adjusting a minimum blocksize as follows.

-   -   If the size (i.e., resolution) of the input image is greater        than or equal to FHD, the luma block is prohibited from being        partitioned into 4×4-sized luma blocks, and the chroma block is        prohibited from being partitioned into 2×2-sized chroma blocks.    -   Specifically, when the size (i.e., resolution) of the input        image is greater than or equal to FHD, the following conditions        may be applied when determining whether to partition the block        QT/BT/TT.    -   When the size (i.e., resolution) of the input image is FHD or        higher, the QT/BT/TT partitioning condition is determined.

1) In the case of 4×4 blocks after QT, horizontal BT, vertical BT,horizontal TT or vertical TT partitioning in the current luma block, thecorresponding partitioning is prohibited.

2) In the case of 2×2 blocks after QT, horizontal BT, vertical BT,horizontal TT or vertical TT partitioning in the current chroma block,the corresponding partitioning is prohibited.

Meanwhile, the QT structure, the BT structure, and the TT structure maybe described later.

FIG. 4 shows an example of partitioning a block through the QTstructure. The QT structure may represent a structure in which a blockhaving a size of 2N×2N is partitioned into four sub-blocks having a sizeof N×N. Referring to FIG. 4, block A may be partitioned into four squaresub-blocks (block A0, block A1, block A2, and block A3) according to theQT structure. In addition, the partitioned block may be partitioned intoblocks of a lower depth recursively by the QT structure. For example,referring to FIG. 4, the sub-block A1 may be partitioned into foursub-blocks (block B0, block B1, block B2, and block B3) according to theQT structure.

FIG. 5 shows an example of partitioning a block through the BTstructure. The BT structure may represent a structure in which aW×H-sized block is partitioned into two (W/2)×H-sized sub-blocks or twoW×(H/2)-sized sub-blocks. The structure in which the W×H-sized block ispartitioned into two (W/2)×H-sized sub-blocks may be expressed as avertical BT structure, and the structure in which the W×H-sized block ispartitioned into two W×(H/2)-sized sub-blocks may be referred to as ahorizontal BT structure.

Referring to FIG. 5, a block B3 that is no longer partitioned by a QTstructure may be partitioned into a sub-block C0 and a sub-block C1 by avertical BT structure, or may be partitioned into a sub-block D0 and asub-block D1 by a horizontal BT structure. In addition, like block C0,each sub-block may be further partitioned into a horizontal BT structure(e.g., sub-block E0, sub-block E1) or a vertical BT structure (e.g.,sub-block F0, sub-block F1) recursively.

FIG. 6 shows an example of partitioning a block through the TTstructure. The TT structure may represent a structure in which aW×H-sized block is partitioned into two (W/4)×H-sized sub-blocks and(W/2)×H-sized sub-blocks, or two W×(H/4)-sized sub-blocks andW×(H/2)-sized sub-blocks. In this case, among the three sub-blocks, a(W/2)×H-sized sub-block or W×(H/2)-sized sub-block may be a centralsub-block. The structure in which the W×H-sized block is partitionedinto two (W/4)×H-sized sub-blocks and (W/2)×H-sized sub-blocks may berepresented as a vertical TT structure, and the structure in which theW×H-sized block is partitioned into two W×(H/4)-sized sub-blocks andW×(H/2)-sized sub-blocks may be represented as a horizontal TTstructure.

Referring to FIG. 6, a block B3 that is no longer partitioned by a QTstructure may be partitioned into a sub-block C0, a sub-block C1, and asub-block C2 by a vertical TT structure, or partitioned into D0,sub-block D1, and sub-block D2 by a horizontal TT structure. Inaddition, like block C1, each sub-block may be further partitionedrecursively through a horizontal TT structure (e.g., partitioned intosub-block E0, sub-block E1, sub-block E2) or vertical TT structure(e.g., sub-block F0, sub-block F1, and sub-block F2).

Meanwhile, the current block may be recursively partitioned according toa quad-tree binary-tree ternary-tree (QTBTTT) structure. For example,the current block may be partitioned into a plurality of coding units ofa deeper depth based on a quad tree structure, a binary tree structure,and/or a ternary structure. The QTBTTT structure may also be referred toas a multi-type tree (MTT) structure.

For example, the current block may be partitioned according to the MTTstructure based on signaled partitioning information.

FIG. 7 exemplarily shows a signaling mechanism of partitioninginformation.

Referring to FIG. 7, a CTU may be treated as a root of a QT, and thus,the CTU may be initially partitioned into the QT structure. Thereafter,each QT leaf node (CU which is no longer partitioned into the QTstructure) may be further partitioned into an MTT structure afterwards.In the MTT structure, a first flag (e.g., MTT split CU flag(mtt_split_cu_flag)) may be signaled to indicate whether a correspondingnode (i.e., the corresponding CU) is additionally partitioned. When thecorresponding node is additionally partitioned (i.e., when the value ofthe first flag is 1), a second flag (e.g., MTT split CU vertical flag(mtt_split_cu_vertical_flag)) may be signaled to indicate a partitioningdirection. That is, the second flag may indicate the partitioningdirection of the corresponding node. Thereafter, a third flag (e.g., MTTsplit CU binary flag (mtt_split_cu_binary_flag)) may be signaled toindicate whether a partition type is binary partitioning or ternarypartitioning. That is, the third flag may indicate whether the partitiontype of the corresponding node is binary partitioning or ternarypartitioning. For example, a multi-type tree partitioning mode(MttSplitMode) of a corresponding CU derived based on the second flagand the third flag may be derived as shown in the following.

TABLE 3 MttSplitMode mtt_split_cu_vertical_flag mtt_split_cu_binary_flagSPLIT_TT_HOR 0 0 SPLIT_BT_HOR 0 1 SPLIT_TT_VER 1 0 SPLIT_BT_VER 1 1

Here, SPLIT_TT_HOR, SPLIT_BT_HOR, SPLIT_TT_VER, and SPLIT_BT_VER mayrepresent a partition type (or a multi-type tree partition mode).Specifically, SPLIT_TT_HOR may represent a horizontal ternary type,SPLIT_BT_HOR may represent a horizontal binary type, SPLIT_TT_VER mayrepresent a vertical ternary type, and SPLIT_TT_VER may represent avertical binary type. Referring to Table 3, when the value of the secondflag is 0 and the value of the third flag is 0, the partition type ofthe corresponding CU may be derived as the horizontal ternary type, whenthe value of the second flag is 0 and the value of the third flag is 1,the partition type of the CU may be derived as the horizontal binarytype, when the value of the second flag is 1 and the value of the thirdflag is 0, the partition type of the corresponding CU may be derived asthe vertical ternary type, and when the value of the second flag is 1and the value of the third flag is 1, the partition type of thecorresponding CU may be derived as the vertical binary type.

FIG. 8 exemplarily shows a partition type in an MTT structure.

Referring to FIG. 8, the horizontal ternary type may be a type in whicha block is partitioned into two W×(H/4)-sized sub-blocks andW×(H/2)-sized sub-blocks, in which the W×(H/2)-sized sub-block of is acentral sub-block. In addition, referring to FIG. 8, the verticalternary may represent a type in which a block is partitioned into two(W/4)×H-sized sub-blocks and (W/2)×H-sized sub-blocks, in which the(W/2)×H-sized sub-block is a central sub-block. Also, referring to FIG.8, the horizontal binary type may represent a type in which a block ispartitioned into two W×(H/2)-sized sub-blocks, and the vertical binarytype may represent a type in which a block is partitioned into two(W/2)×H-sized sub-blocks.

Meanwhile, an embodiment in which the above-described condition isapplied when determining whether to QT/BT/TT partition a block when asize (i.e., resolution) of the input image is greater than or equal toFHD is as follows.

FIG. 9 exemplarily shows an embodiment in which partitioning into a4×4-sized luma block and a 2×2-sized chroma block is prohibited when thesize of an input image is greater than or equal to FHD.

Referring to FIG. 9, the encoding apparatus/decoding apparatus maydetermine whether the number of samples (or the number of pixels) of thecurrent image is 1920×1080 or higher (S900).

When the number of samples of the current image is 1920×1080 or more,the encoding apparatus/decoding apparatus may determine whether thenumber of samples of the block generated by partitioning the currentblock into a QT structure, a BT structure, or a TT structure is greaterthan a specific number (S910). When the current block is a current lumablock, the encoding apparatus/decoding apparatus may determine whetherthe number of samples of the generated blocks by partitioning is greaterthan 16, and when the current block is a current chroma block, theencoding apparatus/decoding apparatus may determine whether the numberof samples of the generated blocks by partitioning is greater than 4.The specific number may be represented as a threshold value.

When the number of samples of the generated blocks by partitioning isgreater than the specific number, the encoding apparatus/decodingapparatus may check the existing QT/BT.TT partitioning condition for thecurrent block and perform partitioning on the current block. (S920).

Alternatively, when the number of samples of the generated blocks bypartitioning is not greater than the specific number, the encodingapparatus/decoding apparatus may not perform partitioning on the currentblock (S930).

Meanwhile, when the number of samples of the current image is less than1920×1080, the encoding apparatus/decoding apparatus may check theexisting QT/BT.TT partitioning condition for the current block withoutthe determination process of step S910, and then perform partitioning onthe current block (S920).

Alternatively, more specifically, an embodiment in which a minimum blocksize is adaptively determined by partitioning an image size (i.e.,resolution) may be proposed. The above embodiment is as follows.

-   -   When a size of an input image is FHD or higher and UHD or        smaller, partitioning into 4×4-sized luma blocks and 2×2-sized        chroma blocks is prohibited.    -   When a size of the input image is UHD or larger, partitioning        into 4×4 size, 4×8 size, 8×4-sized luma blocks and 2×2 size, 4×2        size, and 2×4-sized chroma block is prohibited.

Specifically, when the size (i.e., resolution) of the input imagecorresponds to the above-described condition, the following conditionsmay be applied when determining whether to QT/BT/TT partition a block.

-   -   QT/BT/TT partitioning condition determination when a size of the        input image is greater than FHD and less than UHD

1) If the current luma block becomes a 4×4-sized block after QT,horizontal BT, vertical BT, horizontal TT, or vertical TT partitioning,the corresponding partitioning is prohibited.

2) If the current chroma block becomes a 2×2-sized block after QT,horizontal BT, vertical BT, horizontal TT or vertical TT partitioning,the corresponding partitioning is prohibited.

-   -   QT/BT/TT partitioning condition determination when a size of the        input image is UHD or greater

1) If the current luma block becomes a 4×4-sized, 4×8-sized or 8×4-sizedblock after QT, horizontal BT, vertical BT, horizontal TT or vertical TTpartitioning, the corresponding partitioning is prohibited.

2) If the current chroma block becomes a 2×2-sized, 2×4-sized, or4×2-sized after QT, horizontal BT, vertical BT, horizontal TT orvertical TT partitioning, the corresponding partitioning is prohibited.

According to the present embodiment, by applying different minimum blocksizes in FHD and UHD as described above, it is possible to reduce thethroughput of worst case data during encoding/decoding of UHD video to ¼and at the same time minimize encoding loss.

Meanwhile, when the size (i.e., resolution) of the input image isgreater than or equal to FHD, an embodiment in which the above-describedcondition is applied when determining whether to QT/BT/TT partition ablock is as follows.

FIG. 10 exemplarily shows an embodiment in which a minimum block size isadjusted based on a size of an input image.

Referring to FIG. 10, the encoding apparatus/decoding apparatus maydetermine whether the number of samples (or the number of pixels) of thecurrent image is 1920×1080 or higher (S1000).

When the number of samples of the current image is 1920×1080 or greater,the encoding apparatus/decoding apparatus may determine whether thenumber of samples (or the number of pixels) of the current image is3840×2160 or greater (S1010).

When the number of samples of the current image is 3840×2160 or more,the encoding apparatus/decoding apparatus may set a threshold value forthe current block (S1020). In this case, the threshold value for thecurrent luma block may be set to 32, and the threshold value for thecurrent chroma block may be set to 8. Alternatively, when the number ofsamples of the current image is less than 3840×2160, the encodingapparatus/decoding apparatus may set a threshold value for the currentblock (S1030). In this case, a threshold value for the current lumablock may be set to 16 and a threshold value for the current chromablock may be set to 4.

Thereafter, the encoding apparatus/decoding apparatus may determinewhether the number of samples of the blocks generated by partitioningthe current block into a QT structure, a BT structure, or a TT structureis greater than the set threshold value (S1040).

When the number of samples generated by partitioning the block isgreater than the threshold value, the encoding apparatus/decodingapparatus may check the existing QT/BT.TT partitioning condition for thecurrent block and perform the partitioning on the current block (S1050).

Alternatively, when the number of samples generated by partitioning theblock is not greater than the threshold value, the encodingapparatus/decoding apparatus may not partition partitioning on thecurrent block (S1060).

Meanwhile, when the number of samples of the current image is less than1920×1080, the encoding apparatus/decoding apparatus may check theexisting QT/BT.TT partitioning condition for the current block withoutthe determination process of steps S1010 to S1040, and performpartitioning on the current block (S1050).

Alternatively, an embodiment in which a minimum block size is determinedregardless of size of an input image may be proposed.

As an embodiment, the following scheme may be proposed.

-   -   Partitioning into 4×4-sized luma blocks and 2×2-sized chroma        blocks is prohibited in all-sized input images

Specifically, the following conditions may be applied when determiningwhether a block is partitioned into QT/BT/TT.

-   -   Determine QT/BT/TT partitioning condition in all image sizes

1) If the current luma block becomes a 4×4-sized block after QT,horizontal BT, vertical BT, horizontal TT, or vertical TT partitioning,the partitioning is prohibited.

2) If the current chroma block becomes a 2×2-sized block after QT,horizontal BT, vertical BT, horizontal TT or vertical TT partitioning,the partitioning is prohibited.

FIG. 11 exemplarily shows an embodiment of adjusting the minimum blocksize.

Referring to FIG. 11, the encoding apparatus/decoding apparatus maydetermine whether the number of samples of a block generated bypartitioning a current block into a QT structure, a BT structure, or aTT structure is greater than a threshold value (S1100). When the currentblock is a current luma block, the encoding apparatus/decoding apparatusmay determine whether the number of divided and generated samples of theblock is greater than 16, and when the current block is a current chromablock, the encoding apparatus/decoding apparatus may determine whetherthe number of partitioned and generated samples of the block is greaterthan 4. That is, the threshold value for the current luma block may beset to 16, and the threshold value for the current chroma block may beset to 4. In other words, when the current block is a current lumablock, the encoding apparatus/decoding apparatus may determine whetherthe number of samples of the current block is 32 or less, and when thecurrent block is a current chroma block, the encoding apparatus/decodingapparatus may determine whether the number of samples in the currentblock is 8 or less. That is, the threshold value for the current lumablock may be set to 32, and the threshold value for the current chromablock may be set to 8. When the current block is partitioned, when it ispartitioned according to the BT structure, it is partitioned intosub-blocks including half the number of samples of the current block,and thus, a value of double of the threshold value of the number of thepartitioned and generated samples of the block may be compared with thecurrent block and determined. In addition, when the current block ispartitioned, when the current block is partitioned according to the QTstructure or the TT structure, it is partitioned into sub-blocksincluding a sample number of ¼ of the number of samples of the currentblock, and thus, a value that is four times the threshold of the numberof partitioned and generated samples of the block may be compared withthe current block and determined.

When the number of partitioned and generated samples of the block isgreater than the threshold value (i.e., the number of samples of thecurrent block is less than or equal to the threshold value), theencoding apparatus/decoding apparatus may check the existing QT/BT.TTpartitioning conditions for the current block and perform partitioningon the current block (S1110).

Alternatively, when the number of partitioned and generated samples ofthe block is not greater than the threshold value (that is, when thenumber of samples of the current block is greater than the thresholdvalue), the encoding apparatus/decoding apparatus may not performpartitioning on the current block (S1120).

Alternatively, the following scheme may be proposed as an embodiment.

-   -   Partitioning into 2×2-sized chroma blocks in input image of all        sizes

Specifically, when determining whether to QT/BT/TT partition a block,the following conditions may be applied.

-   -   Determine QT/BT/TT partitioning condition in all image sizes

1) When the current chroma block becomes a 2×2-sized block after QT,horizontal BT, vertical BT, horizontal TT, or vertical TT partitioning,the corresponding partitioning is prohibited.

For example, the encoding apparatus/decoding apparatus may determinewhether the number of samples of a block generated by partitioning thecurrent chroma block into a QT structure, a BT structure, or a TTstructure is greater than a threshold value (e.g., 4). For example, thethreshold value for the current chroma block may be set to 4.

When the number of the partitioned and generated samples of the block isgreater than the threshold value, the encoding apparatus/decodingapparatus may check the existing QT/BT.TT partitioning condition for thecurrent chroma block and perform partitioning on the current chromablock. Alternatively, when the number of partitioned and generatedsamples of the block is not greater than the threshold value, theencoding apparatus/decoding apparatus may not partition partitioning onthe current chroma block.

As in the above-described embodiments, by limiting the minimum blocksize in all input image sizes, encoding and decoding dependent on theinput image may be prevented.

Alternatively, another embodiment may be proposed in which the problemof complexity and high cost in hardware implementation may be solved byadjusting the minimum block size. That is, another embodiment may beproposed in which the data throughput in the worst case is adjusted byadaptively adjusting the minimum block size.

Based on the experimental results shown in Table 2 above, the presentembodiment proposes a method of transmitting minimum block sizeinformation by a high level syntax (HLS) such as a sequence parameterset (SPS), a picture parameter set (PPS), or a slice header. That is,according to the present embodiment, the minimum block size informationindicating the minimum block size may be signaled by the SPS, PPS, orslice header, and block partitioning may be performed based on theminimum block size derived based on the minimum block size information.

For example, the minimum block size information in the SPS may berepresented as shown in the table below. That is, the minimum block sizeinformation signaled by the SPS may be as shown in the following table.

TABLE 4 Descriptor seq_parameter_set_rbsp( ) { sps_seq_parameter_set_idue(v) chroma_format_idc ue(v) if( chroma_format_idc = = 3 )separate_colour_plane_flag u(1) pic_width_in_luma_samples ue(v)pic_height_in_luma_samples ue(v) bit_depth_luma_minus8 ue(v)bit_depth_chroma_minus8 ue(v) qtbtt_dual_tree_intra_flag ue(v)log2_ctu_size_minus2 ue(v) log2_min_qt_size_intra_slices_minus2 ue(v)log2_min_qt_size_inter_slices_minus2 ue(v)log2_min_cu_pixel_num_luma_minus4 ue(v)log2_min_cu_pixel_num_chroma_minus2 ue(v)max_mtt_hierarchy_depth_inter_slices ue(v)max_mtt_hierarchy_depth_intra_slices ue(v) sps_cclm_enabled_flag ue(1)sps_mts_intra_enabled_flag ue(1) sps_mts_inter_enabled_flag ue(1)rbsp_trailing_bits( ) }

The minimum block size information may include minimum luma block sizeinformation and/or minimum chroma block size information. The minimumluma block size information may represent a minimum luma block size, andthe minimum chroma block size information may represent a minimum chromablock size. Referring to Table 4, log 2_min_cu_pixel_num_luma_minus4 andlog 2_min_cu_pixel_num_chroma_minus2 may be included in the SPS. The log2_min_cu_pixel_num_luma_minus4 may indicate a syntax element of theminimum luma block size information, and the log2_min_cu_pixel_num_chroma_minus2 may indicate a syntax element of theminimum chroma block size information.

The decoding apparatus may limit the minimum block size based on the log2_min_cu_pixel_num_luma_minus4 and the log2_min_cu_pixel_num_chroma_minus2.

As an example, when a value of the signaled log2_min_cu_pixel_num_luma_minus4 is 0 and a value of log2_min_cu_pixel_num_chroma_minus2 is 0, a minimum number of samples ofthe luma block represented by log 2_min_cu_pixel_num_luma_minus4 is 16(for example, log 2_num_num_2×4 size) The minimum number of samples ofthe indicated chroma block may be 4 (e.g., 2×2 size). Therefore, theminimum block size limitation may not be performed.

As another example, when the value of the signaled log2_min_cu_pixel_num_luma_minus4 is 1 and the value of log2_min_cu_pixel_num_chroma_minus2 is 1, the minimum number of samples ofthe luma block represented by log 2_min_cu_pixel_num_luma_minus4 may be32 and the minimum number of chroma blocks represented by log2_min_pixel_num_2 samples may be 8. Accordingly, the decoding apparatusmay limit the size of a 4×4-sized luma block and a 2×2-sized chromablock. That is, the decoding apparatus may limit partitioning into a4×4-sized luma block and a 2×2-sized chroma block.

As another example, when the value of the signaled log2_min_cu_pixel_num_luma_minus4 is 0 and the value of log2_min_cu_pixel_num_chroma_minus2 is 2, the minimum number of samples ofluma blocks represented by log 2_min_cu_pixel_num_luma_minus4 may be 16and the minimum number of chroma blocks represented by the log2_pixel_num_num_2 samples may be 16. In this case, the decodingapparatus may not limit the minimum luma block size. In addition, thedecoding apparatus may limit chroma block sizes of 2×2, 2×4, and 4×2sizes. That is, the decoding apparatus may limit partitioning into 2×2,2×4, and 4×2-sized chroma blocks.

FIG. 12 exemplarily shows an embodiment of determining a minimum blocksize based on signaled minimum block size information.

Referring to FIG. 12, the encoding apparatus/decoding apparatus maydetermine whether the current block is a luma block (S1200). That is,the encoding apparatus/decoding apparatus may determine whether thecurrent block is a current luma block or a current chroma block.

When the current block is the current luma block, the encodingapparatus/decoding apparatus may set a threshold value for the currentluma block based on log 2_min_cu_pixel_num_luma_minus4 (S1210). Forexample, the threshold value for the current luma block may be set to16<<log 2_min_cu_pixel_num_luma_minus4. Alternatively, when the currentblock is not the current luma block but is the current chroma block, theencoding apparatus/decoding apparatus may set a threshold value for thecurrent chroma block based on the log 2_min_cu_pixel_num_chroma_minus2(S1220). For example, the threshold value for the current chroma blockmay be set to 4<<log 2_min_cu_pixel_num_chroma_minus2.

Thereafter, the encoding apparatus/decoding apparatus may determinewhether the number of samples of the block generated by partitioning thecurrent block into a QT structure, a BT structure, or a TT structure isgreater than the set threshold value (S1230).

When the number of generated samples by partitioning the block isgreater than the threshold value, the encoding apparatus/decodingapparatus may check the existing QT/BT.TT partitioning condition for thecurrent block and perform partitioning on the current block (S1240).

Alternatively, when the number of generated samples by partitioning theblock is not greater than the threshold value, the encodingapparatus/decoding apparatus may not perform partitioning on the currentblock (S1250).

Meanwhile, the encoding apparatus may perform encoding by setting thevalues of log 2_min_cu_pixel_num_luma_minus4 and log2_min_cu_pixel_num_chroma_minus2 and transmit the information throughSPS. In addition, the encoding apparatus may perform encoding afterperforming the minimum block size limitation based on the set log2_min_cu_pixel_num_luma_minus4 and log 2_min_cu_pixel_num_chroma_minus2.

In addition, the values of log 2_min_cu_pixel_num_luma_minus4 and log2_min_cu_pixel_num_chroma_minus2 may be set according to the image sizeas in the previous embodiment, or the value may be directly set at thetime of encoding and encoding may be performed.

FIG. 13 schematically shows a video encoding method by an encodingapparatus according to the present disclosure. The method disclosed inFIG. 13 may be performed by the encoding apparatus disclosed in FIG. 2.Specifically, for example, steps S1300 to S1320 of FIG. 13 may beperformed by the image partitioner of the encoding apparatus, and S1330may be performed by the entropy encoder of the encoding apparatus. Inaddition, although not shown, a process of deriving a residual samplefor the current block (or a sub-block of the current block) based on theoriginal sample and a predicted sample for the current block (or asub-block of the current block) may be performed by the subtractor ofthe encoding apparatus, a process of deriving reconstructed samples forthe current block (or sub-block of the current block) based on theresidual samples for the current block (or sub-block of the currentblock) and prediction samples may be performed by the adder of theencoding apparatus, and a process of generating information on residualfor the current block (or a sub-block of the current block) based on theresidual sample may be performed by the transformer of the encodingapparatus, and a process of encoding the information on the residual maybe performed by the entropy encoder of the encoding apparatus.

The encoding apparatus determines a partition type for the current block(S1300). The encoding apparatus may partition an input image (orpicture, frame) into one or more processing units. For example, thecurrent block may be recursively partitioned according to a QTBTTT(quad-tree binary-tree ternary-tree) structure from a coding tree unit(CTU) or a largest coding unit (LCU). For example, the current block maybe partitioned into a plurality of sub-blocks based on a QT (Qaud-Tree)type, a horizontal binary type, a horizontal ternary type, a verticalbinary type, and/or a vertical ternary type. The encoding apparatus maydetermine the partition type for the current block as one of the QT(Qaud-Tree) type, the horizontal binary type, the horizontal ternarytype, the vertical binary type, and the vertical ternary type.

The encoding apparatus determines whether to partition the current blockbased on a size of the current block (S1310). The encoding apparatus maydetermine whether to partition the current block based on the size ofthe current block. The size of the current block may represent thenumber of samples of the current block. Alternatively, the size of thecurrent block may represent a width or height of the current block. Forexample, when the partition type of the current block is a verticalbinary type or a vertical ternary type, the size of the current blockmay be a width of the current block, and when the partition type of thecurrent block is a horizontal binary type or a horizontal ternary type,the size of the current block may be a height of the current block.

For example, when the current block is a chroma block and a size of thecurrent block is less than or equal to the minimum chroma block size, itmay be determined that the current block is not partitioned. Inaddition, when the current block is a chroma block and a size of thecurrent block is larger than the minimum chroma block size, it may bedetermined that the current block is partitioned.

For example, when the current block is the chroma block and the size ofa sub-block partitioned and derived from the current block is 2×2, itmay be determined that the current block is not partitioned.

Further, for example, when the current block is a luma block and thesize of the current block is less than or equal to the minimum lumablock size, it may be determined that the current block is notpartitioned. In addition, when the current block is a luma block and asize of the current block is larger than the minimum luma block size, itmay be determined that the current block is partitioned.

For example, when the current block is the luma block and a size of thesub-block partitioned and derived from the current block is 4×4, it maybe determined that the current block is not partitioned.

Meanwhile, the minimum chroma block size may be derived as follows.

As an example, the minimum chroma block size may be derived as a presetvalue. For example, the minimum chroma block size may be 8, 16 or 32.

Alternatively, as an example, the minimum chroma block size may bederived based on information indicating the minimum chroma block size.For example, the encoding apparatus may determine the minimum chromablock size, and generate and encode information indicating the minimumchroma block size, and the minimum chroma block size may be derivedbased on information indicating the minimum chroma block size. Theminimum chroma block size may be derived as 8, 16, or 32 based oninformation indicating the minimum chroma block size.

In addition, the minimum luma block size may be derived as follows.

As an example, the minimum luma block size may be derived as a presetvalue. For example, the minimum luma block size may be 16, 32, or 64.

Alternatively, as an example, the minimum luma block size may be derivedbased on information indicating the minimum luma block size. Forexample, the encoding apparatus may determine the minimum luma blocksize, and generate and encode information indicating the minimum lumablock size, and the minimum luma block size may be derived based on theinformation indicating the minimum chroma block size. For example, theminimum luma block size may be derived as 16, 32, or 64 based on theinformation indicating the minimum luma block size.

When it is determined that the current block is not partitioned, theencoding apparatus does not partition the current block, and when it isdetermined that the current block is partitioned, the encoding apparatuspartitions the current block into sub-blocks based on the partition type(S1320).

For example, when it is determined that the current block ispartitioned, the encoding apparatus may partition the current block intothe sub-blocks according to the partition type. The partition type maybe one of the QT (Qaud-Tree) type, the horizontal binary type, thehorizontal ternary type, the vertical binary type, and the verticalternary type.

The QT type may indicate a type in which a block is partitioned intofour (W/2)×(H/2)-sized sub-blocks. Here, W may denote a width of thecurrent block, and H may be a height of the current block. In addition,the horizontal ternary type may indicate a type in which a block ispartitioned into two W×(H/4)-sized sub-blocks and W×(H/2)-sizedsub-blocks in which the W×(H/2)-sized sub-block is a center sub-block.In addition, the vertical ternary type may indicate a type in which ablock is partitioned into two (W/4)×H-sized sub-blocks and (W/2)×H-sizedsub-blocks in which the (W/2)×H-sized sub-block is a central sub-block.Block-in type may be indicated. In addition, the horizontal binary typemay indicate a type in which a block is partitioned into twoW×(H/2)-sized sub-blocks, and the vertical binary type may indicate atype in which a block is partitioned into two (W/2)×H-sized sub-blocks.

Meanwhile, the encoding apparatus may encode the sub-blocks.

For example, as described above, the encoding apparatus may performprediction on sub-blocks, generate predicted blocks including predictionsamples for the sub-blocks, and generate and encode prediction relatedinformation for sub-blocks. The image information may include theprediction related information. The encoding apparatus may determinewhether intra prediction or inter prediction is applied to each of thesub-blocks, and may determine a specific intra/inter prediction mode foreach sub-block. Next, the encoding apparatus may generate predictionsamples based on various prediction methods described above.

In addition, for example, although not shown, the encoding apparatus mayderive residual samples for the sub-blocks based on the original samplesand prediction samples for the sub-blocks, generate Information on theresidual for the sub-blocks based on the residual samples, and encodethe information on the residual. The image information may include theinformation on the residual. Also, the encoding apparatus may generatereconstructed samples for the sub-blocks based on the prediction samplesand the residual samples for the sub-blocks.

Further, for example, when the current block is not partitioned, theencoding apparatus may decode the current block.

For example, as described above, the encoding apparatus may performprediction on the current block and generate a predicted block includinga prediction sample for the current block, and generate and encodeprediction related information on the current block. The imageinformation may include the prediction related information. The encodingapparatus may determine whether intra prediction or inter prediction isapplied to the current block, and may determine a specific intra/interprediction mode for the current block. Next, the encoding apparatus maygenerate a prediction sample based on various prediction methodsdescribed above.

In addition, for example, although not shown, the encoding apparatus mayderive a residual sample for the current block based on the originalsample and the predicted sample for the current block, generateinformation on residual for the current block based on the residualsample, and encode the information on the residual. Also, the encodingapparatus may generate a reconstructed sample for the current blockbased on the prediction sample and the residual sample for the currentblock.

The encoding apparatus encodes image information including partitioninginformation indicating a partition type for the current block (S1330).The encoding apparatus may encode image information includingpartitioning information indicating a partition type for the currentblock and signal the information through a bitstream.

As an example, the partitioning information may include a first flagindicating whether the current block is partitioned into a QT(Quad-Tree) type or not. Here, the QT type may indicate a partition typein which the current block is partitioned into four (W/2)×(H/2)-sizedsub-blocks. W may denote a width of the current block, and H may denotea height of the current block.

In addition, when the value of the first flag is 0, the partitioninginformation may include a second flag and a third flag. The second flagmay indicate a partitioning direction of the current block, and thethird flag may indicate whether the partition type of the current blockis a binary-tree (BT) type or a tertiary-tree (TT) type. A syntaxelement indicating the first flag may be split_qt_flag, a syntax elementindicating the second flag may be mtt_split_cu_vertical_flag, and asyntax element indicating the third flag may bemtt_split_cu_binary_flag.

In addition, for example, the image information may include informationindicating a minimum luma block size. The information indicating theminimum luma block size may be signaled in units of a coding unit (CU),a slice header, a picture parameter set (PPS), or a sequence parameterset (SPS). That is, the information indicating the minimum luma blocksize may be signaled as a coding unit (CU), a slice header, a pictureparameter set (PPS), or a sequence parameter set (SPS). Also, forexample, the image information may include information indicating aminimum chroma block size. The information indicating the minimum chromablock size may be signaled in units of a coding unit (CU), a sliceheader, a picture parameter set (PPS), or a sequence parameter set(SPS). The information indicating the minimum luma block size may besignaled as a coding unit (CU), a slice header, a picture parameter set(PPS), or a sequence parameter set (SPS). A syntax element indicatinginformation indicating the minimum luma block size may be log2_min_cu_pixel_num_luma_minus4, and a syntax element indicatinginformation indicating the minimum chroma block size may be log2_min_cu_pixel_num_chroma_minus2.

Meanwhile, the image information may include prediction relatedinformation on the current block or the sub-blocks. The predictionrelated information may indicate information on inter prediction orintra prediction applied to the current block or the sub-blocks. Inaddition, the image information may include information on a residualfor the current block or the sub-blocks.

Meanwhile, the bitstream may be transmitted to a decoding apparatusthrough a network or a (digital) storage medium. Here, the network mayinclude a broadcasting network and/or a communication network, and thedigital storage medium may include various storage media such as USB,SD, CD, DVD, Blu-ray, HDD, and SSD.

FIG. 14 schematically shows an encoding apparatus that performs an imageencoding method according to the present disclosure. The methoddisclosed in FIG. 13 may be performed by the encoding apparatusdisclosed in FIG. 14. Specifically, for example, the image partitionerof the encoding apparatus of FIG. 14 may perform S1300 to S1320 of FIG.13, and the entropy encoder of the encoding apparatus of FIG. 14 mayperform S1330 of FIG. 13. In addition, although not shown, the processof deriving a residual sample for the current block (or a sub-block ofthe current block) based on the original sample and the predicted samplefor the current block (or a sub-block of the current block) may beperformed by the subtractor of the encoding apparatus of FIG. 14, theprocess of deriving a reconstructed sample for the current block (or asub-block of the current block) based on a prediction sample and aresidual sample for the current block (or a sub-block of the currentblock) may be performed by the adder of the encoding apparatus of FIG.14, and the process of generating information on the residual for thecurrent block (or a sub-block of the current block) based on theresidual sample may be performed by the transformer of the encodingapparatus of FIG. 14, and the process of encoding the information on theresidual may be performed by the entropy encoder of the encodingapparatus of FIG. 14.

FIG. 15 schematically shows a video decoding method by the decodingapparatus according to the present disclosure. The method disclosed inFIG. 15 may be performed by the decoding apparatus disclosed in FIG. 3.Specifically, for example, S1500 of FIG. 15 may be performed by theentropy decoder of the decoding apparatus, and steps S1510 and S1520 maybe performed by the image partitioner, the predictor, and the adder ofthe decoding apparatus. In addition, although not shown, the process ofacquiring information on the residual of the current block through thebitstream may be performed by the entropy decoder of the decodingapparatus, and the process of deriving the residual sample for thecurrent block based on the residual information may be performed by aninverse transformer of the decoding apparatus.

The decoding apparatus obtains image information including partitioninginformation (S1500). The decoding apparatus may obtain the imageinformation including the partitioning information through a bitstream.

As an example, the partitioning information may include a first flagindicating whether the current block is partitioned into a QT(Quad-Tree) type or not. Here, the QT type may indicate a partition typein which the current block is partitioned into four (W/2)×(H/2)-sizedsub-blocks. W may denote a width of the current block, and H may denotea height of the current block.

In addition, when the value of the first flag is 0, the partitioninginformation may include a second flag and a third flag. The second flagmay indicate a partitioning direction of the current block, and thethird flag may indicate whether the partition type of the current blockis a binary-tree (BT) type or a tertiary-tree (TT) type. A syntaxelement indicating the first flag may be split_qt_flag, a syntax elementindicating the second flag may be mtt_split_cu_vertical_flag, and asyntax element indicating the third flag may bemtt_split_cu_binary_flag.

In addition, for example, the image information may include informationindicating a minimum luma block size. The information indicating theminimum luma block size may be signaled in units of a coding unit (CU),a slice header, a picture parameter set (PPS), or a sequence parameterset (SPS). That is, the information indicating the minimum luma blocksize may be signaled as a coding unit (CU), a slice header, a pictureparameter set (PPS), or a sequence parameter set (SPS). Also, forexample, the image information may include information indicating aminimum chroma block size. The information indicating the minimum chromablock size may be signaled in units of a coding unit (CU), a sliceheader, a picture parameter set (PPS), or a sequence parameter set(SPS). The information indicating the minimum luma block size may besignaled as a coding unit (CU), a slice header, a picture parameter set(PPS), or a sequence parameter set (SPS). A syntax element indicatinginformation indicating the minimum luma block size may be log2_min_cu_pixel_num_luma_minus4, and a syntax element indicatinginformation indicating the minimum chroma block size may be log2_min_cu_pixel_num_chroma_minus2.

Meanwhile, the image information may include prediction relatedinformation on the current block or the sub-blocks. The predictionrelated information may indicate information on inter prediction orintra prediction applied to the current block or the sub-blocks.

The decoding apparatus determines whether to partition the current blockbased on a size of the current block (S1510). The decoding apparatus maydetermine whether to partition the current block based on the size ofthe current block. The size of the current block may represent thenumber of samples of the current block. Alternatively, the size of thecurrent block may represent a width or height of the current block. Forexample, when the partition type of the current block is a verticalbinary type or a vertical ternary type, the size of the current blockmay be a width of the current block, and when the partition type of thecurrent block is a horizontal binary type or a horizontal ternary type,the size of the current block may be a height of the current block.

For example, when the current block is a chroma block and a size of thecurrent block is less than or equal to the minimum chroma block size, itmay be determined that the current block is not partitioned. Inaddition, when the current block is a chroma block and a size of thecurrent block is larger than the minimum chroma block size, it may bedetermined that the current block is partitioned.

For example, when the current block is the chroma block and the size ofa sub-block partitioned and derived from the current block is 2×2, itmay be determined that the current block is not partitioned.

Further, for example, when the current block is a luma block and thesize of the current block is less than or equal to the minimum lumablock size, it may be determined that the current block is notpartitioned. In addition, when the current block is a luma block and asize of the current block is larger than the minimum luma block size, itmay be determined that the current block is partitioned.

For example, when the current block is the luma block and a size of thesub-block partitioned and derived from the current block is 4×4, it maybe determined that the current block is not partitioned.

Meanwhile, the minimum chroma block size may be derived as follows.

As an example, the minimum chroma block size may be derived as a presetvalue. For example, the minimum chroma block size may be 8, 16 or 32.

Alternatively, as an example, the minimum chroma block size may bederived based on the information indicating the minimum chroma blocksize. For example, the minimum chroma block size may be derived as 8, 16or 32 based on the information indicating the minimum chroma block size.

In addition, the minimum luma block size may be derived as follows.

As an example, the minimum luma block size may be derived as a presetvalue. For example, the minimum luma block size may be 16, 32, or 64.

Alternatively, as an example, the minimum luma block size may be derivedbased on the information indicating the minimum luma block size. Forexample, the minimum luma block size may be derived as 16, 32, or 64based on the information indicating the minimum luma block size.

The decoding apparatus decodes the current block or sub-blocks of thecurrent block based on whether to determine the current block asdetermined (S1520).

For example, when it is determined that the current block ispartitioned, the decoding apparatus may partition the current block intosub-blocks based on the partitioning information, and decode thesub-blocks.

For example, when it is determined that the current block is to bepartitioned, the decoding apparatus may derive a partition type for thecurrent block based on the partitioning information, and partition thecurrent block into sub-blocks according to the partition type.

For example, the partitioning information may include a first flag. Whena value of the first flag is 1, the decoding apparatus may partition thecurrent block into the sub-blocks according to the QT type. The QT typemay represent a type in which a block is partitioned into four(W/2)×(H/2)-sized sub-blocks. Here, W may denote a width of the currentblock and H may be a height of the current block.

Further, for example, when the value of the first flag is 0, thedecoding apparatus may partition the current block into sub-blocksthrough the partition type of the current block derived based on thesecond flag and the third flag. The partition type derived based on thefirst flag and the third flag may be one of a horizontal ternary type, ahorizontal binary type, a vertical ternary type, and a vertical binarytype. For example, when the value of the second flag is 0 and the valueof the third flag is 0, the partition type may be derived as thehorizontal ternary type. When the value of the second flag is 0 and thevalue of the third flag is 1, the partition type may be derived as thehorizontal binary type. When the value of the second flag is 1 and thevalue of the third flag is 0, the partition type may be derived as thevertical ternary type, and when the value of the second flag is 1 andthe value of the third flag is 1, the partition type may be derived asthe vertical binary type.

The horizontal ternary type may be a type in which a block ispartitioned into two W×(H/4)-sized sub-blocks and W×(H/2)-sizedsub-blocks, in which the W×(H/2)-sized sub-block of is a centralsub-block. In addition, the vertical ternary may represent a type inwhich a block is partitioned into two (W/4)×H-sized sub-blocks and(W/2)×H-sized sub-blocks, in which the (W/2)×H-sized sub-block is acentral sub-block. Also, the horizontal binary type may represent a typein which a block is partitioned into two W×(H/2)-sized sub-blocks, andthe vertical binary type may represent a type in which a block ispartitioned into two (W/2)×H-sized sub-blocks.

Thereafter, the decoding apparatus may decode the sub-blocks.

For example, as described above, the decoding apparatus may performprediction on the sub-blocks and generate predicted blocks includingprediction samples for the sub-blocks. The decoding apparatus maydetermine whether intra prediction or inter prediction is applied toeach of the sub-blocks based on the prediction related information, andmay determine a specific intra/inter prediction mode for each sub-block.Next, the decoding apparatus may generate prediction samples based onvarious prediction methods described above.

The decoding apparatus may generate reconstructed samples based on theprediction samples. For example, the decoding apparatus may receiveinformation on residual for the sub-blocks from the bitstream. Theinformation on the residual may include a transform coefficient on theresidual sample. The decoding apparatus may derive the residual samples(or residual sample array) for the sub-blocks based on the informationon the residual. In this case, the decoding apparatus may generate thereconstructed samples based on the prediction samples and the residualsamples. The decoding apparatus may derive a reconstructed block or areconstructed picture based on the reconstructed sample. Thereafter, asdescribed above, the decoding apparatus may apply an in-loop filteringprocedure such as deblocking filtering and/or SAO procedure to thereconstructed picture in order to improve subjective/objective imagequality as needed.

Meanwhile, when it is determined that the current block is notpartitioned, the decoding apparatus may decode the current block withoutpartitioning the current block.

For example, as described above, the decoding apparatus may performprediction on the current block and generate a predicted block includinga prediction sample for the current block. The decoding apparatus maydetermine whether intra prediction or inter prediction is applied to thecurrent block based on the prediction related information and maydetermine a specific intra/inter prediction mode for the current block.Next, the decoding apparatus may generate a prediction sample based onvarious prediction methods described above.

The decoding apparatus may generate a reconstructed sample based on theprediction sample. For example, the decoding apparatus may receiveinformation on the residual for the current block from the bitstream.The information on the residual may include a transform coefficient onthe residual sample. The decoding apparatus may derive the residualsample (or residual sample array) for the current block based on theinformation on the residual. In this case, the decoding apparatus maygenerate the reconstructed sample based on the prediction sample and theresidual sample. The decoding apparatus may derive a reconstructed blockor a reconstructed picture based on the reconstructed sample.Thereafter, as described above, the decoding apparatus may apply anin-loop filtering procedure such as deblocking filtering and/or SAOprocedure to the reconstructed picture in order to improvesubjective/objective image quality as needed.

FIG. 16 schematically shows a decoding apparatus for performing a videodecoding method according to the present disclosure. The methoddisclosed in FIG. 15 may be performed by the decoding apparatusdisclosed in FIG. 16. Specifically, for example, the entropy decoder ofthe decoding apparatus of FIG. 16 may perform S1500 of FIG. 15, and theimage partitioner, the predictor, and the adder of the decodingapparatus of FIG. 16 may perform steps S1510 and S1520 of FIG. 15. Inaddition, although not shown, the process of acquiring image informationincluding the information on the residual of the current block throughthe bitstream may be performed by the entropy decoder of the decodingapparatus of FIG. 16. The process of deriving the residual samples forthe current block based on the information on the residual may beperformed by the inverse transformer of the decoding apparatus of FIG.16.

According to the present disclosure, image coding efficiency may beimproved by effectively performing image partitioning.

In addition, according to the present disclosure, it is possible toreduce worst case data throughput by limiting partitioning into lumablocks and/or chroma blocks having a specific size or less, therebyefficiently reducing an encoding and decoding processing rate.

In the above-described embodiment, the methods are described based onthe flowchart having a series of steps or blocks. The present disclosureis not limited to the order of the above steps or blocks. Some steps orblocks may occur simultaneously or in a different order from other stepsor blocks as described above. Further, those skilled in the art willunderstand that the steps shown in the above flowchart are notexclusive, that further steps may be included, or that one or more stepsin the flowchart may be deleted without affecting the scope of thepresent disclosure.

The embodiments described in this specification may be performed bybeing implemented on a processor, a microprocessor, a controller or achip. For example, the functional units shown in each drawing may beperformed by being implemented on a computer, a processor, amicroprocessor, a controller or a chip. In this case, information forimplementation (e.g., information on instructions) or algorithm may bestored in a digital storage medium.

In addition, the decoding apparatus and the encoding apparatus to whichthe present disclosure is applied may be included in a multimediabroadcasting transmission/reception apparatus, a mobile communicationterminal, a home cinema video apparatus, a digital cinema videoapparatus, a surveillance camera, a video chatting apparatus, areal-time communication apparatus such as video communication, a mobilestreaming apparatus, a storage medium, a camcorder, a VoD serviceproviding apparatus, an Over the top (OTT) video apparatus, an Internetstreaming service providing apparatus, a three-dimensional (3D) videoapparatus, a teleconference video apparatus, a transportation userequipment (e.g., vehicle user equipment, an airplane user equipment, aship user equipment, etc.) and a medical video apparatus and may be usedto process video signals and data signals. For example, the Over the top(OTT) video apparatus may include a game console, a blue-ray player, aninternet access TV, a home theater system, a smart phone, a tablet PC, aDigital Video Recorder (DVR), and the like.

Furthermore, the processing method to which the present disclosure isapplied may be produced in the form of a program that is to be executedby a computer and may be stored in a computer-readable recording medium.Multimedia data having a data structure according to the presentdisclosure may also be stored in computer-readable recording media. Thecomputer-readable recording media include all types of storage devicesin which data readable by a computer system is stored. Thecomputer-readable recording media may include a BD, a Universal SerialBus (USB), ROM, PROM, EPROM, EEPROM, RAM, CD-ROM, a magnetic tape, afloppy disk, and an optical data storage device, for example.Furthermore, the computer-readable recording media includes mediaimplemented in the form of carrier waves (e.g., transmission through theInternet). In addition, a bit stream generated by the encoding methodmay be stored in a computer-readable recording medium or may betransmitted over wired/wireless communication networks.

In addition, the embodiments of the present disclosure may beimplemented with a computer program product according to program codes,and the program codes may be performed in a computer by the embodimentsof the present disclosure. The program codes may be stored on a carrierwhich is readable by a computer.

FIG. 17 illustrates a structural diagram of a contents streaming systemto which the present disclosure is applied.

The content streaming system to which the embodiment(s) of the presentdisclosure is applied may largely include an encoding server, astreaming server, a web server, a media storage, a user device, and amultimedia input device.

The encoding server compresses content input from multimedia inputdevices such as a smartphone, a camera, a camcorder, etc. Into digitaldata to generate a bitstream and transmit the bitstream to the streamingserver. As another example, when the multimedia input devices such assmartphones, cameras, camcorders, etc. directly generate a bitstream,the encoding server may be omitted.

The bitstream may be generated by an encoding method or a bitstreamgenerating method to which the embodiment(s) of the present disclosureis applied, and the streaming server may temporarily store the bitstreamin the process of transmitting or receiving the bitstream.

The streaming server transmits the multimedia data to the user devicebased on a user's request through the web server, and the web serverserves as a medium for informing the user of a service. When the userrequests a desired service from the web server, the web server deliversit to a streaming server, and the streaming server transmits multimediadata to the user. In this case, the content streaming system may includea separate control server. In this case, the control server serves tocontrol a command/response between devices in the content streamingsystem.

The streaming server may receive content from a media storage and/or anencoding server. For example, when the content is received from theencoding server, the content may be received in real time. In this case,in order to provide a smooth streaming service, the streaming server maystore the bitstream for a predetermined time.

Examples of the user device may include a mobile phone, a smartphone, alaptop computer, a digital broadcasting terminal, a personal digitalassistant (PDA), a portable multimedia player (PMP), navigation, a slatePC, tablet PCs, ultrabooks, wearable devices (ex. Smartwatches, smartglasses, head mounted displays), digital TVs, desktops computer, digitalsignage, and the like. Each server in the content streaming system maybe operated as a distributed server, in which case data received fromeach server may be distributed.

What is claimed is:
 1. A video decoding method performed by a decodingapparatus, comprising: obtaining image information includingpartitioning information; determining whether a current block ispartitioned based on a size of the current block; and decoding thecurrent block based on whether the determined current block ispartitioned, wherein based on the current block i-s-being a chroma blockand the size of the current block i-s-being less than or equal to aminimum chroma block size, it is determined that the current block isnot partitioned, wherein the partitioning information includes a firstflag indicating whether the current block is partitioned as quad-tree(OT) type, and based on a value of the first flag being 0, thepartitioning information includes a second flag and a third flag, thesecond flag indicates a partitioning direction of the current block, andthe third flag indicates whether a partition type of the current blockis a binary-tree (BT) type or ternary-tree (TT) type.
 2. The videodecoding method of claim 1, wherein when the current block is the chromablock and a size of a sub-block partitioned and derived from the currentblock is 2×2, it is determined that the current block is notpartitioned.
 3. The video decoding method of claim 1, wherein the sizeof the current block indicates the number of samples of the currentblock.
 4. The video decoding method of claim 3, wherein the minimumchroma block size is
 16. 5. The video decoding method of claim 4,wherein the image information includes information indicating theminimum chroma block size, and the minimum chroma block size is derivedbased on information indicating the minimum chroma block size.
 6. Thevideo decoding method of claim 1, wherein when the current block is aluma block and the size of the current block is equal to or smaller thanthe minimum block size, it is determined that the current block is notpartitioned.
 7. The video decoding method of claim 6, wherein the imageinformation includes information indicating a minimum luma block size,and the minimum luma block size is derived based on informationindicating the minimum luma block size.
 8. The video decoding method ofclaim 7, wherein the information indicating the minimum luma block sizeis signaled as a sequence parameter set (SPS).
 9. The video decodingmethod of claim 1 wherein the current block is partitioned intosub-blocks based on the partition type of the current block derivedbased on the second flag and the third flag.
 10. The video decodingmethod of claim 9, wherein when the value of the second flag is 0 andthe value of the third flag is 0, the partition type is derived as ahorizontal ternary type, when the value of the second flag is 0 and thevalue of the third flag is 1, the partition type is derived as ahorizontal binary type, when the value of the second flag is 1 and thevalue of the third flag is 0, the partition type is derived as avertical ternary type, and when the value of the second flag is 1 andthe value of the third flag is 1, the partition type is derived as avertical binary type.
 11. A video encoding method performed by anencoding apparatus, the video encoding method comprising: determining apartition type for a current block; determining whether the currentblock is partitioned based on a size of the current block; partitioningthe current block into sub-blocks based on the partition type based ondetermination that the current block is partitioned; and encoding imageinformation including partitioning information indicating the partitiontype for the current block, wherein based on the current block is beinga chroma block and the size of the current block is being less than orequal to a minimum chroma block size, it is determined that the currentblock is not partitioned, wherein the partitioning information includesa first flag indicating whether the current block is partitioned asquad-tree (QT) type, and based on a value of the first flag being 0, thepartitioning information includes a second flag and a third flag, thesecond flag indicates a partitioning direction of the current block, andthe third flag indicates whether a partition type of the current blockis a binary-tree (BT) type or ternary-tree (TT) type.
 12. The videoencoding method of claim 11, wherein, when the current block is thechroma block and a size of a sub-block partitioned and derived from thecurrent block is 2×2, it is determined that the current block is notpartitioned.
 13. The video encoding method of claim 11, wherein the sizeof the current block indicates the number of samples of the currentblock.
 14. The video encoding method of claim 13, wherein the minimumchroma block size is
 16. 15. A non-transitory computer-readable storagemedium storing a bitstream generated by a method, the method comprising:determining a partition type for a current block; determining whetherthe current block is partitioned based on a size of the current block;partitioning the current block into sub-blocks based on the partitiontype based on determination that the current block is partitioned; andencoding image information including partitioning information indicatingthe partition type for the current block; and generating the bitstreamincluding the image information, wherein based on the current blockbeing a chroma block and the size of the current block being less thanor equal to a minimum chroma block size, it is determined that thecurrent block is not partitioned, wherein the partitioning informationincludes a first flag indicating whether the current block ispartitioned as quad-tree (QT) type, and based on a value of the firstflag being 0, the partitioning information includes a second flag and athird flag, the second flag indicates a partitioning direction of thecurrent block, and the third flag indicates whether a partition type ofthe current block is a binary-tree (BT) type or ternary-tree (TT) type.